1. Technical Field
The invention relates generally to cold cathode luminescent field emission devices and, particularly, to a field emission lamp employing a getter to exhaust unwanted gas from therein, thereby ensuring a high degree of vacuum. The invention also relates to a method for making a field emission lamp.
2. Discussion of Related Art
Electrical lamps for daily living are usually incandescent lamps and/or fluorescent lamps. Ever since Thomas Edison invented the first viable incandescent lamps in 1879, the incandescent lamps have a long history for simple fabrication thereof. However, because an incandescent lamp emits light by incandescence of a tungsten filament, most of electric energy used therein is converted into heat and thereby is wasted. Therefore, a main drawback of the incandescent lamp is the low energy efficiency thereof.
A typical conventional fluorescent lamp generally includes a transparent glass tube. The transparent glass tube has a white or colored fluorescent material coated on an inner surface thereof and a certain amount of mercury vapor filled therein. In use, electrons are accelerated by an electric field and the accelerated electrons collide with the mercury vapor. This collision causes excitation of the mercury vapor and causes radiation of ultraviolet rays. The ultraviolet rays irradiate the fluorescent material, whereby the ultraviolet rays are converted into visible light. Compared with the incandescent lamps, the fluorescent lamps have higher electrical energy utilization ratios. However, when the glass tube is broken, the mercury vapor is prone to leak out and, thus, is poisonous and noxious to humans and is environmentally unsafe.
To settle the above problems, a kind of fluorescent lamps (i.e., field emission lamps) not adopting the mercury vapor has been developed. A conventional field emission lamp without the mercury vapor generally includes a cathode and an anode. The cathode has a number of nanotubes formed on a surface thereof, and the anode has a fluorescent layer facing the nanotube layer of the cathode. In use, a strong electrical field is provided to excite the nanotubes. A certain amount of electrons is then accelerated and emitted from the nanotubes, and such electrodes collide with the fluorescent layer of the anode, thereby producing visible light.
For a field emission lamp, a high degree of vacuum in an inner portion (i.e., interior) thereof is a virtual necessity. In general, the better of the degree of vacuum of the field emission lamp is able to maintain during the sealing process and thereafter during use, the better of the field emission performance thereof is. To maintain the degree of vacuum of the field emission lamp within a desired range, a conventional way is to provide a getter in the inner portion thereof. Such a getter is able to exhaust a gas produced by the fluorescent layer and/or any residual gas remaining within the field emission lamp upon sealing and evacuation thereof. The getter is generally selected from a group consisting of non-evaporable getters and evaporable getters.
For the evaporable getter, a high temperature evaporating process has to be provided during the fabrication of the field emission lamp, and a plane arranged in the inner portion of the field emission lamp has to be provided to receive the evaporated getter. Thus, the cost of the fabrication of the field emission lamp increases, and the cathode and anode are prone to shorting during the high temperature evaporating process, thereby causing the failure of the field emission lamp. For the non-evaporable getter, it is generally focused in a position away from the cathode. Thus, the degree of vacuum of portions near to the cathode tends to be poorer, in the short-term, than that of portions near to the getter, at least until internal equilibrium can be reached, thereby decreasing the field emission performance of the cathode or at least potentially resulting in a fluctuating performance thereof.
What is needed, therefore, is a field emission lamp that overcomes the above-mentioned shortcomings to ensure a high degree of vacuum thereof, thus providing a better and more steady field emission performance during the use thereof.
What is also needed is a method for making such a field emission lamp.